Method for shielding electronic equipment by coating with copper containing composition

ABSTRACT

A new copper dispersion coating composition particularly useful as a copper shielding coating for plastic enclosures to protect electronic equipment from electromagnetic interference (EMI). The coating maintains high electrical conductivity even after exposure to heat, humidity or salt spray. The coating composition may also be used as a one-coat air dry system that is spray applied and needs no protective overcoat.

This is a division of application Ser. No. 60,771, filed July 26, 1979,now U.S. Pat. No. 4,305,847.

BACKGROUND OF THE INVENTION

This invention broadly relates to a new coating composition and to amethod of applying said coating composition to various enclosures toprotect electronic equipment from electromagnetic interference (EMI).More particularly this invention relates to a new copper dispersioncoating composition usable as a copper shielding coating that maintainshigh electrical conductivity even after exposure to heat, humidityand/or salt spray; and thereby, it eliminates many of the shortcomingsof other copper coatings that have been attempted for this purpose. Thenew coating composition of this invention may be applied as a one-coatair dry system that is spray applied and needs no protective overcoat.It also of course may be applied by other means such as brushing,dipping or the like.

The state of the art is indicated by the following: U.S. Pat. Nos.2,750,303; 2,980,719; 3,074,818; 3,142,814; 3,382,203; 3,998,993;4,123,562; 2,750,307; 3,501,353; 3,532,528; 3,653,931; 3,867,738;3,867,739; 3,716,427; 3,060,062; German Pat. No. 1,941,328; and AchesonColloids Co. product data sheets on Electrodag 112, 414, 424, and 433.

It has been known that copper particles dispersed in a binder resinmaterial or solution could be used to make an electrically conductivecoating. However all of the prior coatings of this type have had themajor deficiency that during storage or during usage, the copperoxidizes and the electrical properties changed such that there was adetrimental effect. Under many usage conditions this electrical propertychange is of such magnitude that the formerly conductive coating becomesan insulating coating. Attempts to overcome this change of electricalproperties have called for replacement of the copper conductiveparticles with the more expensive noble-metals such as silver, gold andthe platinum group, all of which greatly and significantly increase thecost of the electrically conductive coating. Thus a copper dispersioncoating has long been sought after, which when applied in film form to asubstrate, would provide good electrical conductance properties evenafter exposure to elevated temperatures for substantial time periods.

Another proposed solution which has been investigated in the past is thetreatment of the copper particle to prevent its oxidation and subsequentchange in electrical properties. Some of the solutions that have beensuggested are treatment of the copper with chemicals such asnitrosobenzene, benzotriazole, chromium salts, silicates, and the like.Other treatments suggested have included high molecular weight alcoholsand stearates. These attempted solutions have been ineffective ortemporary at best. In addition many of these surface treatments resultedin the copper particle becoming an electrical insulator rather than thedesired electrical conductor.

Accordingly a main object of this invention is to provide a new coatingcomposition containing finely particulated copper particles and whichcomposition is suitable for use in forming applied coatings having verygood electrical conductance properties.

Another important object of this invention is to provide a novel methodof forming EMI shielding coatings on enclosures for electronicequipment.

Another object of the invention is to provide a new copper coatingcomposition which when applied as a coating maintains high electricalconductivity even after exposure to heat, humidity or salt spray.

Another object of the invention is to provide an environmentally stableair dry copper coating.

Another object of the invention is to provide a new copper coatingcomposition which provides controlled electrical properties.

Another object of the invention is to provide a novel method ofprotecting electronic equipment from electromagnetic interference (EMI)by applying a copper shielding coating to enclosures for the equipment.

Other objects, features and advantages of the present invention willbecome apparent from the subsequent description and the appended claims.

SUMMARY OF THE INVENTION

A significant purpose of this invention is to describe a method ofmaking an electrically conductive coating composition containing copperparticles which coating composition has a long storage life and yet thecoating still retains highly useful electrical conductance propertiesafter exposure to elevated temperatures for significant periods of time.By elevated temperatures it is meant temperatures in the range of 160°F., and/or temperatures up to as high as approximately 200° F. or higherin some instances. The uses for these new compositions includeelectromagnetic interference shielding; production of printed circuitsby silk screening, and similar uses where a highly conductive filmcoating is needed.

Numerous prior art deficiencies have been overcome through the discoverythat if finely divided copper particles are co-mixed with specialorganic titanates as described herein, the copper particles do notappear to degrade and the conductivity of the deposited film remainsstable over a long period of time even at the elevated temperaturesencountered in many specialized uses. Although the discovery of thisinvention has been used primarily to preserve the desirable electricalproperties of the copper in such applied coatings or films, it has alsobeen discovered that an improved decorating effect is also obtained bymeans of the non-oxidizing copper coatings which are disclosed herein.

DESCRIPTION OF PREFERRED EMBODIMENTS

While it is not fully understood as to why the invention operates toprovide such significantly useful electrically conductive coppercoatings, particularly in the area of EMI shielding coatings, thefollowing preferred embodiments and preferred aspects of the inventionwill now be described.

The new compositions discovered and disclosed herein have the desirablefeatures of ease in manufacturing, long shelf life, ease of application,and most importantly, have acceptable electrical properties even whenused at elevated temperatures.

The pigment material used in the coating composition is substantially ofcopper. For example the pigment material is substantially pureelectrical grade copper and/or it may be such as an electrical gradecopper alloy. Normally the copper particles used herein are of 95%purity or greater and preferably they are of 99% purity or greater.

The pigment particle size broadly stated should be under 200 microns inaverage particle size and preferably it is under 50 microns averageparticle size.

The binder resin used in the coating composition can be any one of anumber of different materials. The binder resin is preferably athermoplastic resin material which is compatible with the copperparticles and with the titanate material used in the coatingcomposition. Thermosetting resin materials may also be used as thebinder resin herein. The binder resin is selected from at least one ofthe group consisting of thermoplastic acrylic, vinyl, urethane, alkyd,polyester, hydrocarbon, fluoroelastomer and celluosic resins; and,thermosetting acrylic, polyester, epoxy, urethane, and alkyd resins. Thebinder resin material chosen should generally be one which is easilyused for spray coating applications, and also it should be non-reactivewith the copper and non-reactive with the titanate.

The pigment to binder ratio by weight in the coating composition of theinvention should broadly be within the range between about 20 to 1 andabout 2 to 1, and preferably it should be maintained in the rangebetween about 10 to 1 and about 4 to 1.

The organic titanate material used in the coating composition is onewhich provides good heat stability to the coating as applied on asubstrate, and it enables the coating to maintain good electricalconductivity during sustained exposure to elevated temperatures. Theorganic titanate used in the composition should be present within thebroad range of about 1/2% to about 18% by weight of the pigment materialin the composition. Preferably it should be within the range of about 2%to about 12% by weight of the pigment material, and best results areobtained within the range of about 3% to about 10%. The organic titanateshould preferably be a pyrophospate type, with best results beingobtained with an organic titanate which is of the pyrophosphate typeselected from at least one of the group consisting of monoalkoxytitanates of titanium chelates. As described herein the organic titanatematerial enables the coating as applied to maintain an electricalconductivity of under 10 ohms per square at one mil applied filmthickness after exposure to an elevated temperature of about 160° F. forsubstantial time periods. Preferred results can be obtained, using thecoatings as described herein, of under 5 ohms per square. For someapplications, conductivity values up to 150 ohms per square aresatisfactory, but for most electrical uses, resistance values belowabout 10 ohms per square are desirable.

Particularly useful organic titanates for use in the coating compositionof this invention are the following:

(1) isopropyl tri(dioctylpyrophosphato) titanate

(2) titanium di(dioctylpyrophosphate) oxyacetate

(3) tri(butyl, octyl pyrophosphato) isopropyl titanate mono(dioctyl,hydrogen phosphite)

(4) titanium di(butyl, octyl pyrophosphate) di (dioctyl, hydrogenphosphite) oxyacetate

(5) di(butyl, methyl pyrophosphato), isopropyl titanate mono(dioctyl,hydrogen) phosphite

(6) di(butyl, methyl pyrophosphato) ethylene titanate mono(dioctyl,hydrogen phosphate)

The organic solvent carrier used with the coatings are conventionalorganic solvents or solvent blends useful for dissolving or dispersingthe binder resin. Because of the known tendency of the organic titanatesto react with water, the solvent carrier should be of very low watercontent or substantially water free. Also because one use of the coatingcomposition is to obtain an electromagnetic interference shield on theinterior surfaces of plastic enclosed electronic devices, the solventblend used should be one which is not only compatible with the resin andcopper particles but also with the plastic containers and one which willnot degrade the plastic materials. For example with many solventsensitive plastics a blend of isopropanol and toluol has been founddesirable. For ease of application, it is generally desirable to use thecoating composition at a low total solids level. Many of theconventional solvents such as ketones, alcohols, acetates, etc. can beused as diluents. Generally suitable solvents are the ketones,aromatics, alcohols, aliphatics or blends of same.

Other materials which may also optionally be present in the coatingcomposition are for example various thixotropic agents selected from atleast one of the group consisting of finely divided silicas or hydratedsilicates. The thixotropic agent when used may be present in the amountof about 0.1% up to about 7% by weight of the total solids andpreferably within the range of about 0.1% to about 5% by weight.Particular materials for this purpose are the Bentone clays and fumedcollidal silicas such as Cab-O-Sil.

The percent total solids in the coating composition should broadly bewithin the range of about 20% up to about 85% by weight, and preferablywithin the range of about 40% to about 80% by weight.

In the following examples the formulating process was maintainedessentially the same for comparative purposes. In addition to the smallsize shot mills, larger equipment such as ball mills, pebble mills,attritors (continuous or batch processing types), high shear mixers andthe like can be used.

In order to further illustrate the invention the following examples areprovided. It is to be understood however that the examples are includedfor illustrative purposes and are not intended to be limiting of thescope of the invention as set forth in the subjoined claims.

EXAMPLE NO. 1*

    ______________________________________                                        Thermoplastic Methyl/Butyl Methacrylate                                       Copolymer Resin                                                               (Acryloid B-66)            10.0                                               Titanium Di(Dioctylpyrophosphate) Oxyacetate                                  KR-138S Organic Titanate   5.4                                                Toluol                     30.0                                               Copper powder                                                                 RL500 (Copper Pigment)     60.0                                               Denatured Ethyl Alcohol                                                       (Jaysol)                   10.0                                               ______________________________________                                    

Formulating Procedure:

(1) Predisperse titanate and resin in solvents.

(2) Load all ingredients in 8 oz. shot mill and mix for 15 minutes.

Results for 1 mil thick applied coating:

Initial Resistance--0.412 ohms per square at 1 mil.

One hour at 160° F.--0.520 ohms per square at 1 mil.

24 hours at 160° F.--0.700 ohms per square at 1 mil.

Test coatings made by spraying on clean glass substrate and air drying24 hours for initial reading and afterdrying for stated intervals.

EXAMPLE NO. 2

    ______________________________________                                        Ethyl Methacrylate Resin                                                      Acryloid B-72             10.0                                                Copper Powder                                                                 MD 750 Copper Pigment     40.0                                                Toluol                    20.0                                                Methyl Ethyl Ketone       20.0                                                Di(Butyl, Methyl Pyrophosphato), Isopropyl                                    Titanate Mono(Dioctyl, Hydrogen) Phosphite                                    KR 62ES (Ken-Rich)        5.0                                                 Fumed Colloidal Silica                                                        (Cabosil M-5)             0.5                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--9.93 ohms per square at 1 mil.

One hour at 160° F.--13.4 ohms per square at 1 mil.

24 hours at 160° F.--34.5 ohms per square at 1 mil.

EXAMPLE NO. 3

    ______________________________________                                        Methyl Methacrylate Resin                                                     Acryloid A-11             7.0                                                 Copper Particles                                                              RL500                     70.0                                                Methyl Ethyl Ketone       20.0                                                Methyl Isobutyl Ketone    20.0                                                Isopropyl Tri(Dioctylpyrophosphato) Titanate                                  KR38S Organic Titanate (Ken-Rich)                                                                       1.4                                                 Bentonite Clay                                                                Bentone 27                2.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--0.616 ohms per square at 1 mil.

One hour at 160° F.--0.616 ohms per square at 1 mil.

24 hours at 160° F.--0.716 ohms per square at 1 mil.

EXAMPLE NO. 4

    ______________________________________                                        Thermoplastic Vinyl Resin                                                     Union Carbide Corp. - VAGH                                                                              10.0                                                Copper Particles                                                              RL500                     120.0                                               Butyl Acetate             60.0                                                Di(Butyl, Methyl Pyrophosphato), Isopropyl                                    Titanate Mono(Dioctyl, Hydrogen) Phosphite                                                              8.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--2.92 ohms per square at 1 mil.

One hour at 160° F.--2.82 ohms per square at 1 mil.

24 hours at 160° F.--4.00 ohms per square at 1 mil.

EXAMPLE NO. 5

    ______________________________________                                        Thermoplastic Vinyl Resin                                                     Union Carbide Corp. - VYND                                                                              5.0                                                 Copper Particles                                                              RL500                     50.0                                                Methyl Ethyl Ketone       40.0                                                Titanium Di(Butyl, Octyl Pyrophosphato)                                       Di(Dioctyl, Hydrogen Phosphite) Oxyacetate                                    KR158FS                   5.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--10.24 ohms per square at 1 mil.

One hour at 160° F.--11.56 ohms per square at 1 mil.

24 hours at 160° F.--14.88 ohms per square at 1 mil.

EXAMPLE NO. 6

    ______________________________________                                        Rosin-Ester Coating Resin                                                     Cellolyn 102              5.4                                                 Ethyl Cellulose           5.4                                                 Butanol                   3.2                                                 Xylol                     2.2                                                 Methyl Ethyl Ketone       16.7                                                Butyl Acetate             11.0                                                Copper Powder                                                                 RL500                     50.0                                                Di(Butyl, Methyl Pyrophosphato), Isopropyl                                    Titanate Mono(Dioctyl, Hydrogen) Phosphite                                    KR62ES                    9.0                                                 Fumed Colloidal Silica                                                        Cab-O-Sil M-5             1.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--0.563 ohms per square at 1 mil.

One hour at 160° F.--0.605 ohms per square at 1 mil.

24 hours at 160° F.--0.735 ohms per square at 1 mil.

EXAMPLE NO. 7

    ______________________________________                                        Methyl Methacrylate Resin                                                     Acryloid A-11             5.0                                                 Toluol                    30.0                                                Di(Butyl, Methyl Pyrophosphato), Isopropyl                                    Titanate Mono(Dioctyl, Hydrogen) Phosphite                                    KR62ES                    8.0                                                 Bentonite Clay                                                                Bentone 34                1.5                                                 Copper Powder                                                                 RL500                     60.0                                                ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--0.184 ohms per square at 1 mil.

One hour at 160° F.--0.196 ohms per square at 1 mil.

24 hours at 160° F.--0.208 ohms per square at 1 mil.

EXAMPLE NO. 8

    ______________________________________                                        Ethyl Cellulose           8.0                                                 Xylol                     49.0                                                Butanol                   3.0                                                 Denatured Ethyl Alcohol   10.0                                                Tri(Butyl, Octyl Pyrophosphato) Isopropyl                                     Titanate Mono(Dioctyl, Hydrogen Phosphite)                                    KR58FS                    6.0                                                 Copper Powder                                                                 RL500                     40.0                                                ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--0.584 ohms per square at 1 mil.

One hour at 160° F.--0.604 ohms per square at 1 mil.

24 hours at 160° F.--0.660 ohms per square at 1 mil.

EXAMPLE NO. 9

    ______________________________________                                        Nitrocellulose            4.2                                                 Toluol                    3.2                                                 Ethanol                   12.0                                                Copper Powder                                                                 RL500                     36.0                                                Titanium Di(Butyl, Octyl Pyrophosphate)                                       Di(Dioctyl, Hydrogen Phosphite) Oxyacetate                                    KR158FS                   1.8                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--3.2 ohms per square at 1 mil.

One hour at 160° F.--3.2 ohms per square at 1 mil.

24 hours at 160° F.--3.2 ohms per square at 1 mil.

EXAMPLE NO. 10

    ______________________________________                                        Methyl Methacrylate Resin                                                     Elvacite 2008             10.0                                                Cellulose Acetate Butyrate                                                    CAB 381-20                0.5                                                 Copper Powder                                                                 RL500                     50.0                                                Toluol                    20.0                                                Methyl Ethyl Ketone       24.5                                                Titanium Di(Butyl, Octyl Pyrophosphate)                                       Di(Dioctyl, Hydrogen Phosphite) Oxyacetate                                    KR158FS                   8.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coatings:

Initial Resistance--1.63 ohms per square at 1 mil.

One hour at 160° F.--1.71 ohms per square at 1 mil.

24 hours at 160° F.--1.93 ohms per square at 1 mil.

EXAMPLE NO. 11

    ______________________________________                                        Thermoset Acrylic Resin                                                       Acryloid AT-50            20.0                                                Toluol                    10.0                                                Copper Powder                                                                 RL500                     69.0                                                Isopropyl Tri(Dioctylpyrophosphato) Titanate                                  KR-38S                    6.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Cured 20 min. at 300° F.

Results for 1 mil thick applied coating:

Initial Resistance--0.124 ohms per square at 1 mil.

One hour at 160° F.--0.128 ohms per square at 1 mil.

24 hours at 160° F.--0.128 ohms per square at 1 mil.

EXAMPLE NO. 12

    ______________________________________                                        Cellulose Acetate Butyrate                                                    CAB 381-20                5.0                                                 Copper Powder                                                                 RL500                     40.0                                                Methyl Ethyl Ketone       49.0                                                Di(Butyl, Methyl Pyrophosphato), Isopropyl                                    Titanate Mono(Dioctyl, Hydrogen) Phosphite                                    KR62ES                    3.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coatings:

Initial Resistance--0.728 ohms per square at 1 mil.

One hour at 160° F.--0.796 ohms per square at 1 mil.

24 hours at 160° F.--0.928 ohms per square at 1 mil.

EXAMPLE NO. 13

    ______________________________________                                        Methyl Methacrylate Resin                                                     Acryloid B-82             5.0                                                 Copper Powder                                                                 RL500                     90.0                                                Di(Butyl, Methyl Pyrophosphato), Isopropyl                                    Titanate Mono(Dioctyl, Hydrogen) Phosphite                                    KR62ES                    7.0                                                 Toluol                    40.0                                                Isopropanol               10.0                                                Colloidal Fumed Silica                                                        Cabosil M-5               1.5                                                 Butanol                   5.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--1.28 ohms per square at 1 mil.

One hour at 160° F.--1.38 ohms per square at 1 mil.

24 hours at 160° F.--2.15 ohms per square at 1 mil.

EXAMPLE NO. 14

    ______________________________________                                        Polyester Desmophen 1300  10.0                                                Copper Powder                                                                 RL500                     50.0                                                Tri(Butyl, Octyl Pyrophosphato) Isopropyl                                     Titanate Mono(Dioctyl, Hydrogen) Phosphite                                    KR58FS                    6.5                                                 Methyl Ethyl Ketone       10.0                                                Butyl Acetate             20.0                                                Polyisocyanate                                                                Mondur CB-75              18.0                                                ______________________________________                                    

Formulating Procedure:

(1) Disperse KR58FS in solvents and load with RL500 and Des. 1300 in 8oz. shot mill for 15 minutes.

(2) Add Mondur CB-75 and mix thoroughly.

Results for 1 mil thick applied coating:

Initial Resistance--24.9 ohms per square at 1 mil.

One hour at 160° F.--24.5 ohms per square at 1 mil.

24 hours at 160° F.--29.4 ohms per square at 1 mil.

EXAMPLE NO. 15

    ______________________________________                                        Vinyl Resin                                                                   Union Carbide Corp. VAGH  8.0                                                 Copper Powder                                                                 RL500                     60.0                                                Methyl Isobutyl Ketone    40.0                                                Titanium Di(Octylpyrophosphate) Oxyacetate                                    KR138S                    8.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--0.616 ohms per square at 1 mil.

One hour at 160° F.--0.736 ohms per square at 1 mil.

24 hours at 160° F.--0.952 ohms per square at 1 mil.

EXAMPLE NO. 16

    ______________________________________                                        Polyester Coating Resin                                                       INOLEX 5171-200           10.0                                                Copper Powder                                                                 RL500                     80.0                                                Toluol                    30.0                                                Di(Butyl, Methyl Pyrophosphato), Isopropyl                                    Titanate Mono(Dioctyl, Hydrogen) Phosphite                                    KR62ES                    9.0                                                 Polyisocyanate                                                                Desmodur N-75             9.0                                                 ______________________________________                                    

Formulating Procedure:

(1) Predisperse titanate in solvents.

(2) Load blend with RL500 and polyester for 15 minutes in 8 oz. shotmill.

(3) Combine with polyisocyanate.

Results for 1 mil thick applied coating:

Initial Resistance--2.4 ohms per square at 1 mil.

One hour at 160° F.--2.54 ohms per square at 1 mil.

24 hours at 160° F.--3.02 ohms per square at 1 mil.

EXAMPLE NO. 17

    ______________________________________                                        Thermosetting Epoxy Resin                                                     Epon 1001                 7.0                                                 Urea Resin                                                                    Uformite F-492            3.0                                                 Toluol                    20.0                                                Methyl Ethyl Ketone       20.0                                                Copper Powder                                                                 RL500                     70.0                                                Di(Butyl, Methyl Pyrophosphato) Ethylene                                      Titanate Mono(Dioctyl, Hydrogen Phosphate)                                    KR262ES                   5.0                                                 Bentonite                                                                     Bentone 27                1.0                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Cured 15' at 300° F.

Results for 1 mil thick applied coating:

Initial Resistance--8.4 ohms per square at 1 mil.

One hour at 160° F.--8.4 ohms per square at 1 mil.

24 hours at 160° F.--11.2 ohms per square at 1 mil.

EXAMPLE NO. 18

    ______________________________________                                        Thermosetting Polyester Resin                                                 Cyplex 1600               18.0                                                Urea Curative Resin                                                           Beetle 80                 3.0                                                 para-toluenesulfonic acid                                                     PTSA                      0.2                                                 Copper Powder                                                                 RL500                     140.0                                               Di(Butyl, Methyl Pyrophosphato) Ethylene                                      Titanate Mono(Dioctyl, Hydrogen Phosphate)                                    KR262ES                   9.0                                                 Toluol                    10.0                                                Butyl Acetate             10.0                                                Ethylene Clycol Monoethyl Ether                                               Cellosolve                10.0                                                ______________________________________                                    

Formulating Procedure same as Example 1.

Cured 60' at 300° F.

Results for 1 mil thick applied coating:

Initial Resistance--137.6 ohms per square at 1 mil.

One hour at 160° F.--136.0 ohms per square at 1 mil.

24 hours at 160° F.--136.0 ohms per square at 1 mil.

EXAMPLE NO. 19

    ______________________________________                                        Methyl/Butyl Methacrylate Copolymer                                           Acryloid B-66              13.6                                               Copper Powder                                                                 RL500 Copper Pigment       54.3                                               Toluol                     18.3                                               Ethanol                                                                       Jaysol                     9.2                                                Titanium Di(Dioctylpyrophosphate) Oxyacetate                                  KR 138S                    4.5                                                ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--0.417 ohms per square at 1 mil.

One hour at 160° F.--0.447 ohms per square at 1 mil.

24 hours at 160° F.--0.498 ohms per square at 1 mil.

EXAMPLE NO. 20

    ______________________________________                                        Methyl/Butyl Methacrylate Copolymer                                           Acryloid B-66             13.6                                                Copper Powder                                                                 RL500 Pigment             55.0                                                Toluol                    18.3                                                Ethanol                                                                       Jaysol                    5.0                                                 Ethylene Glycol Monoethyl Ether                                               Cellosolve                4.3                                                 Bentonite                                                                     Bentone 34                1.5                                                 Tri(Butyl, Octyl Pyrophosphato) Isopropyl                                     Titanate Mono(Dioctyl, Hydrogen Phosphite)                                    KR-58FS                   2.3                                                 ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coating:

Initial Resistance--0.129 ohms per square at 1 mil.

One hour at 160° F.--0.144 ohms per square at 1 mil.

24 hours at 160° F.--0.159 ohms per square at 1 mil.

EXAMPLE NO. 21

    ______________________________________                                        Thermoplastic Fluoroelastomer Resin                                           Viton                     10.0                                                Butyl Acetate             50.0                                                Titanium Di(Butyl, Octyl Pyrophosphate)                                       Di(Dioctyl, Hydrogen Phosphite) Oxyacetate                                    KR158FS                   5.0                                                 Copper Powder                                                                 RL500 Copper Pigment      80.0                                                Methyl Ethyl Ketone       20.0                                                ______________________________________                                    

Formulating Procedure same as Example 1.

Results for 1 mil thick applied coatings:

Initial Resistance--13.6 ohms per square at 1 mil.

One hour at 160° F.--18.4 ohms per square at 1 mil.

24 hours at 160° F.--26.4 ohms per square at 1 mil.

While it will be apparent that the preferred embodiments of theinvention disclosed are well calculated to fulfill the objects abovestated, it will be appreciated that the invention is susceptible tomodification, variation and change without departing from the properscope or fair meaning of the subjoined claims.

What is claimed is:
 1. A method for shielding an electronic devicehaving an enclosure associated therewith, said method being comprised ofprotecting said device from electromagnetic interference (EMI) byapplying to said enclosure a coating composition comprised of,a pigmentmaterial substantially of copper said pigment being finely particulatedand having a particle size of less than about 200 microns, a binderresin, the pigment to binder weight ratio in said composition beingbetween about 20 to 1 and about 2 to 1, an organic titanate material ofthe pyrophosphate type for providing good heat stability to the coatingas applied to the enclosure,said organic titanate being present inamount of about 1/2% to about 18% by weight of said pigment material,and, an organic solvent carrier for the composition, said compositioncontaining a weight percent total solids within a range of about 20% toabout 85%.
 2. The method of claim 1 further characterized in that,saidorganic titanate is a pyrophosphate type selected from at least one ofthe group consisting of monoalkoxy titanates or titanium chelates. 3.The method of claim 1 further characterized in that,said pigment tobinder ratio is between about 10 to 1 and about 4 to 1, said organictitanate is present between about 2% and about 12% by weight of saidpigment material, said percent total solids is between about 40% andabout 80%.
 4. The method of claim 1 further characterized in that,saidpigment has a particle size of less than about 50 microns.
 5. The methodof claim 1 further characterized in that,said composition additionallycontains a thixotropic agent selected from at least one of the groupconsisting of finely divided silicas, or hydrated silicates,saidthixotropic agent being present between about 0.1% and 7% by weight ofthe total solids.
 6. The method of claim 1 further characterized inthat,said binder resin of is a thermoplastic resin.
 7. The method ofclaim 1 further characterized in that,said binder resin is athermoplastic acrylic resin.
 8. The method of claim 1 furthercharacterized in that,said organic titanate material means enables thecoating as applied to maintain an electrical conductivity of under 10ohms per square at 1 mil applied film thickness after exposure to anelevated temperature of about 160° F. for substantial time periods. 9.The method of claim 1 further characterized in that,said organictitanate material enables the coating as applied to maintain anelectrical conductivity of under 150 ohms per square at 1 mil appliedfilm thickness after exposure to an elevated temperature of about 160°F. for substantial time periods.